Process of chemical metal plating and baths therefor



United States Patent Claims. (cl. 106--1) The present invention relates to improved processes of chemical metal plating of metal or plastic articles employing bath with boron compounds with reducing agents and to improved baths therefor.

Chemical plating baths for the production of metal coatings on metal or plastic surfaces are known. As re ducing agents there are used for this purpose sodium hypophosphite, alkali metal borohydride or boron compounds which carry 1 to 3 hydrogen atoms at the boron atom. The reduction with sodium hypophosphite is expediently carried out in the presence of buffer substances such as sodium citrate, sodium tartrate etc. When an alkali metal borohydride, such as sodium borohydride (NaBH is used as reducing agent, the process is carried out in aqueous alkaline solutions with the addition of complex formers such as ammonia, ethanolamine etc. Organic borohydride compounds with 1 to 3 H-atoms at the boron atom, for example Borazanes (amine boranes), having the formula R NBH Borazenes, having the formula R N=BR Borazines, having the formula RN=BH Borazoles, having the formula (RN-BR) (wherein R represents alkyl, aryl or H, but at least one of the substituents at the B atom is H) may be used in acidic as well as in aqueous alkaline or aqueous solutions. Here also buiier substances are used in acidic solutions, complex formers and possibly buffer substances in alkaline solutions.

Compared with the process using sodium hypophosphite, the chemical plating with alkali metal borohydride is substantially more economical, although in the hitherto known processes the reduction yield according to the equation amounts only to about 20%.

The object of the invention is to provide baths for depositing metals on plastic or metal surfaces, which contain salts of the metals to be deposited and borohydride compounds with 1 to 4 hydrogen atoms directly linked with boron, and are characterized by a content of at least one element of Groups IIb, IIIb, IVb, Vb and/ or VIb of the Periodic System of Elements. (See Lehrbuch fiir anorganische Chemie, edited by E. Wiberg, 37-39, edition 1956, page 443). Moreover, acidic baths contain buffer substances known as such, alkaline baths contain complex formers and, if desired, bufier substances.

The present invention is predicated upon the discovery that by the addition of compounds of elements of Groups IIb, IIIb, IVb, Vb and/or IV!) of the Periodic System to plating baths containing as reducing agent borohydride compound-s with 1 to 4 H-atoms at the boron atom, the

reduction yields and/or plating rate are substantially intheoretical; an addition of stannous chloride to a bath 3,295,999 Patented Jan. 3, 1967 of the same composition gives reduction yields of 37% of the theoretical. With plating baths containing N,N'- diethylborazane as reducing agent and giving a reduction yield of about 19% of the theoretical according to the equation:

an addition of, for example 300 mg. of Tl HAsO leads to reduction yields of 27%.

The plating rates are doubled or even tripled. For example, in an alkali metal borohydride bath without addition and with the use of 0.6 g. NaBH, per litre and a ratio surface is sq. cm./ bath volume in cc.=0.4 NaB-I-L, can no longer be detected only after 40 minutes of .plat ing; with an addition of 200 mg. of SnC-l -2H O/litre to a bath of the same composition, the plating is already terminated after 15 minutes.

At certain concentrations, the metal additives are moreover excellent lustre formers.

The elements of Groups IIb, IIIb, IVb, Vb and/or VIb of the Periodic System, such as nickel, cobalt, iron, zinc, arsenic, thallium, tin, cadmium or lead, can be added to the plating bath in the form of their dissolved salts, e.g. chlorides, sulphates, nitrates, acetates etc., individually or in combination with one another. It is immaterial whether the additive is added to the plating bath as cation, e.g. SnCl -2H O; as anion, e.g. sodium arsenate, or as salt of two effective elements, e.g. TlHAsO A combination of two or more compounds as additive to plating baths is often advantageous. For example, As O when added to a borohydride plating bath in an alkaline solution, yields reduction results of 30% of the theoretical only after an addition of mg. As O /litre, whereas a combination with thallium added as Tl HAsQ, yields results of more than 40% of the theortical already at 60 mg./litre. This effect of increased reduction yield and plating rate is surprising in so far as it is known from the literature that heavy metal salts decompose alkali metal borohydride solutions.

Metals, such as nickel, copper alloys, aluminum, iron as well as plastic material such as articles from acetyl cellulose, cellulose-acetobutyrate, polyvinylchloride, or polyethylene, can be plated with these new baths. The content of the baths of salts of the plating metals such as sulphates, chlorides, acetates etc. of, for example, nickel, cobalt, iron, zinc etc., corresponds to the values already known for borohydrideor borazane-containing baths.

The plating metal salt concentration of the bath solu tion is about 30 g./litre and the boron compound concentration being about 0.1-10 g./litre to a ratio surface in cmF/bath volume in cm. =0.4. The absolute concentration of the boron compound in the bath expressed in mol/ litre is within the range of 0.011.5, the molar ratio of the metal salt of the plating metal to the boron compound in said bath is within the range 0.012.0 (metal salt/ boron compound=0.012.0) and the molar ratio of the .metal salt of the plating metal to the salt or doublesalt of elements of Group IIb, IIIb, IVb, Vb and VIb of the Periodic System is within the range 0.0010.1 (metal salt/ double salt=0.001-0.1).

As reducing agents for the chemical depositing of metal there can be used for example:

(1) Alkali metal borohydrides such as sodium borohydride;

(2) Water-soluble B-H compounds, e.g., N,N',N"-trimethylborazane, N,N-dimethyl-borazane, N,N- dimethylborazene;

. (3) B-H compounds which have been rendered watersOluble by the addition of solubilizers, e.g., N,N-diethylborazane, N-isopropyl-borazene, N-isopropyl-bo razine, N-

trimethylborazole. Solubilizers are, for example, methanol, dioxan, etc.

As buffer substances for these plating baths there may be used, for example, sodium acetate, sodium citrate, sodium tartrate etc. I

Suitable complex formers are, for example, ammonia, ethylene diamine, ethanolamine etc.

The chemical plating of metal or plastic surfaces in the new plating baths presents advantages as follows:

(a) Improved utilisation of the reducing agent and thus reducing the costs of the process.

(b) Increased rate of depositing and thus reducing the time of stay of the object to be plated in the plating bath.

The coatings obtained on metal or plastic surfaces are smooth, brilliant and adherent.

The following examples are given for the purpose of illustrating the invention.

Example 1 1 litre of a plating bath consisting of 30 g./litre NiCl .6H O, 40 g./litre NaOH, 50 g./litre C H (NH 70 mg./litre TlNO is heated to 90 C., 2 brass plates and 2 copper plate with a surface of 1 sq. dm./plate are suspended therein and 0.6 g. NaBH dissolved in about 50 ml. of bath solution, are added. The NaBH content of the solution is established b iodometric analysis before the start and after termination of the plating. The plating is completed after about 20 minutes. coating. of a total of 1.5187 g./4 sq. dm. is obtained on all plates, the consumption of NaBH being 0.5700 g. This corresponds to a NaBH, reduction yield of 43.1%. With increasing addition of TINO the following reduction yields are obtained:

Reduction yield, TlNO /litre of bath liquor, mg.: percent Example 2 3 To 1 litre of a plating bath of the composition of 30 g./ litre NiCl .6H O, 40 g./litre NaOH and 50 g./litre C H (NH heated to 90 C., 220 mg. SnCl .2H O are added, 4 iron plates with a surface of 1 sq. dm./ plate are suspended therein and 0.6 g. NaBH dissolved in 50 ml. of bath solution, are added. The plating is terminated after 15 minutes. A brilliant nickel coating of a total of 1.2959 g. is obtained on all plates, the NaBH consumption being 0.5700 g. This correspond to a reduction yield of 36.8%.

With increasing addition of SnCl .2H O the following reduction yields are obtained:

Reduction yield,

A brilliant Ni-B 4 Example 3 From a plating bath as described in Examples 2, the following reduction yields are obtained by the addition of increasing amounts of As O using a surface/volume ratio of 0.4:

Mg. As O /litre bath liquor: Reducing agent, percent Example 4 Acetyl cellulose foils are treated succesively in the following baths:

(a) 100 g. of sodium hydroxide+0.3 g. of wetting agent+900 g. of water, time of stay: 5 minutes, temperature 5060 C.

(b) 100 g./litre of stannous chloride-F200 cc./litre of cone. hydrochloric acid-{-02 g. of wetting agent, time of stay: 5 minutes, temperature 50-60 C.

(c) 0.5 g./litre of palladium chloride-H0 cc./litre of cone. hydrochloric acid, time of stay 5 minutes, tempera tu-res 20-30 C.

Four foils with a thickness of 100 treated in this way are cut so that their surface amounts to 1 sq. dm./ foil and suspended in a plating bath of the composition given in Example 2. 180 mg. of SbCl are added to the plating bath which is heated to C. and 0.6 g. NaBH dissolved in 50 ml. of bath solution, are added. The surface in sq.'crn./bath volume in cc. ratio is 0.4. A brilliant adherent nickel-boron coating of a total of 1.3114 g. is obtained on all foils, the NaBH consumption being 0.5890 g. This corresponds to a reduction yield of 35.9 g,

With increasing SbCl content in the plating bath the following reduction yields are obtained. The surface/ volume ratio is 0.4.

Mg. SbCl litre bath liquor: Reduction yield, percent Example 5 By the addition of PbCI 8e0 TeO CdCl to 1 litre each of plating bath as indicated in Example 2, the following reduction yields are obtained using a surface/vol ume ratio of 0.4:

(a) Mg. PbCl /l litre of Percent reduction By the addition of TlNO and SnCl .2H O in a proportion by weight of 1:1 to 1 litre of a plating bath as described in Example 2 using a surface/volume ratio=0.4 there are obtained the following reduction yields:

Mg. (SnCl .2H O TINO Percent reduction (1:1) per litre of bath liquor: yield Example 7 An addition of Tl HAsO to 1 litre of a plating bath as described in Example 2 using a surface/volume ratio :04 gives the following reduction yields:

Mg. Tl HAsO per litre of bath Percent reduction liqzuor: yield 23.3

Example 8 To a plating bath of the composition of 30 g. NiCl .6H O, g. of ammonium chloride, 10 g. of sodium citrate, 20 g. of sodium acetate and 950 cc. of water, heated to 70 C., are added 250 mg. of thallium nitrate and 4 metal plates with a surface of 1 sq. dm./plate are suspended therein. The pH value is 5.0. After the addition of 50 ml. of a solution of 3.400 g. of N,N-diethylborazane in methanol, a highly brillant coating of a total of 1.9052 g. Ni is obtained on all plates within 30 minutes. This corresponds to a reduction yield of 27.8% of the theoretical.

With increasing T1NO addition, the following reduction yields are obtained (surface/volume=0.4):

Mg. TlNO Percent reduction yield Example 9 Four foils of cellulose-acetobutyrate with a surface of 1 sq. dm./foil and a thickness of pre-treated as described in Example 4, are suspended in a plating bath of the composition 30 g. NiCl .6H O, 5 g. of ammonium chloride, 10 g. of sodium citrate, 20 g. of sodium acetate and 950 cc. of water at 70 C. i

200 mg. of Tl HAsO and 50 ml. of a solution of 3.1920 g. of N,N-diethylborazane in methanol are added thereto. The pH value is 5. A highly brilliant Ni-coating of a total of 1.6883 g. is obtained on all four foils. This corresponds to a reduction yield of 26.2% of the theoretical.

With increasing Tl HAsO addition, the following reduction yields are obtained:

Mg. Tl HAsO per litre of bath Percent reduction Example 10 By the addition of (a) SnCl .2H O (b) arsenous acid to a plating bath as described in Example 8, the following reduction yields are obtained using a surface/volume ratio =0.4:

(a) Mg. SnCl .2H O/1 litre of bath Percent reduction liquor: yield Percent reduction yield (b) Mg. arsenous acid litre of bath liquor:

We claim:

1. An aqueous metal and plastic plating bath for plating by chemical reduction consisting essentially of 30 g./ 1

and 0.6 g./l. NaBH.;.

2. An aqeous metal and plastic plating bath for plating by chemical reduction, consisting of 30 g./l. NiCl .6H O, 50 g./l. C H (NH 20-250 mg./l. of a mixture of TINO and SnCl .2H O in a proportion by weight of 1:1, and 0.6 g./l. NaBH.;.

3. An aqueous metal and plastic plating bath for plating by chemical reduction, consisting of 30 g./l. NiCl .6H O, 50 g./l. C H (NH 20-150 mg./1. Tl HAsO and 0.6 g./l, NaBH.,.

4. An aqueous metal and plastic plating bath for plating by chemical reduction consisting essentially of 30 g. NiC l .6H O, 5 g. ammonium chloride, 10 g. sodium citrate, 20 g. sodium acetate, 250 mg. thallium nitrate, 3.4 g. N,N'-diethylborazane in the form of its solution in 50 ml. methanol and 950 cc. of water.

NiCl .6H O, 5 g. ammonium chloride, "10 g. sodium citrate, 20 g. sodium acetate, 20-900 mg. Tl HAsO 3.1920 g. N,N-diethylborazane in the form of its solution in methanol, and 950 cc. of Water.

References Cited' by the Examine:

UNITED STATES PATENTS 4 Wesley et"al.- 20449 2,884,344 4/1959 Ramirez 1061X 2,898,379 7/1959 Chambei'lain etal.- '260583X 2,990,296 6/1961 H6ke, 106-1 X 2,994,369 8/1961 Carlen 1061 3,062,666 11/1962 McLeo'd '1061 3,096,182 7/1963 8 FOREIGN-PATENTS 9/1961 Canada. 6/1'96'0 Great Britain.

OTHER REFERENCES L'anges Handbook of Chemistry, pages 56 and 57, 9th edition, 1956-.

, Wm. Scheckter, C. B. Jackson, and Roy M. Adams: Boron Hydrides and Related Compounds, 2nd ed., Callery'Chemical Company, 1954..

MORRIYSVLIVEBMAN, Primarj'y Examiner.

Examiners.

I. E. CARSON, J. E. CALLAGI-I'AN, L. B. HAYES, Assistant Examiners. 

2. AN AQUEOUS METAL AND PLASTIC PLATING BATH FOR PLATING BY CHEMICAL REDUCTION, CONSISTING OF 30G./L. NICL2.6H2O, 50 G./L. C2H4(NH2)2, 20-250 MG./L. OF A MIXTURE OF TINO2 AND SNCL2.2H2O IN A PROPORTION BY WEIGHT OF 1:1, AND 0.6 G./L. NABH4. 